Which of the following can be used to access the command line?

The BIOS (Basic Input/Output System) is firmware that initializes hardware during boot; it has its own setup interface but does not provide access to the operating system command line.

A terminal or terminal emulator (such as gnome-terminal, xterm, or konsole) provides a text-based interface to the shell, giving users direct access to the command line. It interprets keyboard input and passes commands to the shell (e.g., bash), displaying text output in return.

X Window System (X11) is a graphical display server framework; it provides the foundation for a GUI but is not itself a command-line interface, though terminal emulators can run within it.

Firefox is a graphical web browser used for accessing websites; it does not provide access to the operating system command line.

xargs is a command-line utility that builds and executes commands from standard input; it is used within the command line but is not a means to access the command line itself.